The Spaniard believes his summer signing does not always get the credit his ability deserves because of the understated nature of his influence.
The 23-year-old Republic of Ireland international sealed a 13 million pound move from the DW Stadium, following Martinez to Goodison Park, and he has impressed during the club's rise to fifth in the Premier League table.
McCarthy has made 20 appearances this season, forming a solid partnership with Gareth Barry in midfield, but his Spanish boss believes that his impact can sometimes go unnoticed.
"James is one of those players you sometimes don't appreciate but he's always there making sure the team has the right balance and what it needs," Martinez told The Liverpool Echo. "He allows others to shine. He can adapt to different situations during a game when you need him to because of the tactical awareness that he has.
"James never plays according to his age because of the incredible amount of experience he already has at 23."
Everton travels to White Hart Lane on Sunday for a crunch clash with fellow Champions League chaser Tottenham.